Radaring Titan

The Cassini spacecraft carried the European Space Agency’s Huygens probe to Saturn and released it in December 2004. The probe landed on Titan Jan. 14, 2005, acquiring a set of images using the descent imager/spectral radiometer camera as it parachuted to the surface.

As Cassini continued to orbit Saturn, its imaging science subsystem and visual and infrared mapping spectrometer mapped the region where the Huygens probe landed. On Friday, Oct. 28, 2005, Cassini’s radar instrument provided the highest resolution orbital data yet of this area.

The two images above tell the story. On the left, in color, is a composite of the imaging camera and infrared data (red areas are brighter and blue darker, as seen in infrared). On the right is the synthetic aperture radar image. The Huygens descent images are shown inset on the left image and outlined in yellow on the right. The magenta cross in both images shows the best estimate of the actual Huygens landing site. This is a preliminary result, based on the best information available at the present time.

In the left image, the brighter areas seen by the Huygens camera correspond to the large area depicted in red and yellow. On closer inspection, bright features within the Huygens mosaic seem to correspond to smaller features in the map composed of data from the visual and infrared spectrometer and imaging camera. On the right, the correspondence is less clear. In radar images bright features are usually rougher, so one would not necessarily expect an obvious connection.

This set of global images show the areas mapped so far on Saturn’s moon Titan by the Cassini Radar Mapper using its Synthetic Aperture Radar imaging mode and the location of the Oct. 28, 2005, Titan flyby. Labels represent the approximate central longitude of each globe.

The radar swaths are superimposed on a false-color image made from observations by NASA’s Hubble Space Telescope. The top image shows radar swaths from the first Titan flyby, on Oct. 26, 2004, (northernmost) and the second radar pass of Titan, on Feb. 15, 2005 (near-equatorial). The Oct. 26 swath is about 4,500 kilometers long (2,800 miles), extending from 133 degrees west longitude and 32 degrees north latitude through 12 degrees west and 29 degrees north. The February swath is centered at approximately 30 degrees north and 70 degrees west. The spatial resolution of the radar images ranges from about 300 meters (980 feet) per pixel to about 1.5 kilometers (0.93 miles) per pixel.

The middle globe shows the radar swath acquired during the third radar pass, on Sept. 7, 2005, close to Titan’s south pole. The swath is centered at 12 degrees west and 51 degrees south, with similar spatial resolution to the previous two.

These first three radar passes revealed a variety of geologic features, including impact craters, wind-blown deposits, channels, and cryovolcanic features.

The third globe at the bottom shows the location of the radar swath for the Oct. 28 flyby that is detailed above. The location of the Huygens landing site is marked in red. The overlap between the Huygens data and the radar data will give new clues to the nature of the surface seen by the Huygens probe, which landed on Titan in January 2005.